High strength steel



p 1960 D. J. SCHMATZ ET AL 2,934,463

HIGH STRENGTH STEEL Filed April 17, 1959 4 Sheets-Sheet 1 g INVENTORS By KW ATTORNE s April 1960 D. J. SCHMATZ EI'AL 2,934,463

HIGH STRENGTH STEEL 4 Sheets-Sheet 2 Filed April 17, 1959 VI MBA N K R YCm SS Z WM 0 C N JV KQ T H 0% N w o 0 m m Y A m l B m R m 0 m E 8 T N N M O W 2 M m R T T E T W G Fm? E a n m m F m U O T L F HM E u 0 M 0 .l E m. S U A T M- u m m O O 0 O O O 0 O m m m m w 6 mo umDP mmmEwh ATTORNEYS Apnl 26, 1960 D. J. SCHMATZ ETAL 2,934,463

HIGH STRENGTH STEEL Filed April 17, 1959 4 Sheets-Sheet 3 EFFECT OF DEFORMATION ON MECHANICAL PROPERTIES OF AUSFORMED STEELS lo 480 I l x 0.48 c 3Cr l m 0.75Mn 2 Mo I I 5 90%DEF. 5 o- 90% DEF. E 360 w 50% DEF.

a 320 ,...o- 50% DEF. E 0% DEF. :5 280 i a SJ-'--o- 0% DEF. d 240- I i s 0%DEE E 6 g 4 90 A. DEE

m o l l l l TEMPERING TEMPERATURE, F

FEG. 3

D.J. SCHMATZ J.C. SHYNE V. F. ZACKAY INVENTOR.

ATTORNEYS April 26, 1960 D. J. SCHMATZ ETAL 2,934,463

HIGH STRENGTH STEEL Filed April 17, 1959 4 Sheets-Sheet 4 0.4l C, 2.0 Cr, L5 Si, LO Mn, I.O Ni, 0.4 Mo,O.3V

8 400 NO DEFORMATION 15% DEE 93% DEF. Z ULTIMATE E ULTIMATE 300 I/YIELD O d ll||l|llll |llllIlllllllll 200 400 600 e00 200 400 600 200 400 600 800 TEMPERING TEMPERATURE F FIG. 4

D. J. SCHMATZ J. C. SHYNE V. F. ZACKAY INVENTOR.

ATTORNEYS HIGH STRENGTH STEEL Duane J. Schmatz, Dearborn, John C. Shyne, Belleville, and Victor F. Zackay, Dearborn, Mich., assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Application April 17, 1959, Serial No. 807,231

22 Claims. (Cl. 148-31) This is a continuation-in-part of our application Serial Number 726,485, filed April 4, 1958.

Thisinvention isdirected to a class of high strength steels and to the heat treatment employed to obtain the optimum physical properties from these steels. This invention makes possible the production of very high strength steels in articles having a substantial minimum dimension as contrasted to wire and strip. The steels produced by this invention are characterized by a very high tensile strength and a high ratio of yield point to tensile strength. This invention is further concerned with a heat treating method in which the above enumerated valuable properties are obtained in combination with substantial ductility as expressed in terms of elongation and reduction of area so that products produced from such steel find ready commercial acceptance.

This invention is designed as an improvement upon the process-described by Lips et al. in Metal Progress, August 1954, pages 103 and 104. This invention is also to be distinguished from the teachings of United States Letters Patent 2,435,511, issued February 3, 1945, to R. E. Rice and 2,717,846, issued September 13, 1955, to Harvey.

This invention has been developed for use with steels which exhibit a temperature region below the pearlite transformation temperature and above the bainite transformation temperature in which the metastable austenite is comparatively stable, even under conditions of substantial working for a protracted period of time. The following three steels are given by way of examples of steels possessing such a stable austenite.

Chormium appears to be the most effective, most economical and generally desirable element whose addition to a steel composition will increase the temperature range covered by the temperature region mentioned supra and also increase the depth of such a temperature region along the time axis in the usual TTT diagram. These steels and their equilibrium isothermal transformation properties are detailed in a Supplement to Atlas of Isothermal Transformation Diagrams published in 1953 by the United States Steel Corporation at pages 216, 221 and 224 respectively. An inspection of the isothermal transformation diagrams presented for these steels will show that each steel is characterized by a temperature region adjacent 900 Fahrenheit in which metastable austenite can exist without transformation for at least an hour and in many cases for much longer periods of time under normal conditions. The behavior of these metastable austenitic steels under conditions of stress has been expounded upon at length by Bhattacharyya and Kehl in two scholarly articles published recently in the Transactions of the AmericanSociety for Metals. The first articleappears in 2,934,453 Fatented Apr. 26, 1960 the'1955 volume and begins at page 351 and the'second article appears in 1956 and begins at page 234. These articles reflect the universally held opinion that the wealth of information presented in the conventional TTT diagrams while valid for normal conditions is completely inapplicable to metastable austenite while under working conditions. The data appearing upon pages 358 and 359 of the 1955 article is thought to be particularly enlightening. Here specifically dealing with an A181 4340 steel a stress of only 60,000 pounds per square inch is stated to foreshorten the beginning of an isothermal transformation at 845 F. by a factor of four and to similarly effect the termination of the transformation time by a factor of ten thousand to one hundred thousand. Data of this type has discouraged the art from attempting extensive working of steels in the metastable austenitic condition since the stresses introduced by heavy reductions would far exceed the value of 60,000 pounds per square inch and the unwanted transformation of austenite into high temperature decomposition products seemed inevitable.

Despite this data, steel compositions exhibiting a wide bay between the pearlite transformation zone and the bainite transformation zone have been very heavily worked in this selected temperature region while in a metastable austenitic state and have remained austenitic for suflicient time to permit all necessary working operations, even including a reheating operation. The amount of'plasticjdeformation has even been carried beyond the extreme value of ninety-three per cent with a rapid improvement being noted beyond twenty-five per cent reduction. After this extensive working the material is quenched to the martensitic transformation zone and permitted to transform to martensite. When properly tempered, the steel composition so produced demonstrates unique physical and microstructural characteristics.

To aid in an understanding of this invention four figures of drawing have been presented in which:

Figure 1 is an electron microscope photomicrograph of a typical steel composition produced according to the instant invention and magnified 40,000 times.

Figure 2 is a typical TTT diagram for a steel having a bay or deformation range in which austenite is metastable and can be heavily worked without inducing transformation in this temperature range to non-austenitic isothermal decomposition-products. Particular attention is invited to the fact that the time scale along the abscissa is logarithmic. This is, of course, a normal showing and not to be applied to dynamic or working conditions. For the sake of clarity, a curve has been applied to this figure of drawing depicting a typical operation of the invention.

Figure 3 has been added to graphically depict the remarkable physical properties obtained upon tempering steel articles which have been drastically deformed in the metastable austenitic state and then quenched to give a predominantly martensitic structure. Attention is invited to the sharp increase in yield point of these steels as the tempering is increased. A steel of relatively low alloy content demonstrates a yield point of almost 400,000 pounds per square inch, while retaining an elongation of almost five per cent.

Figure 4 of the drawings is almost self-explanatory and has been presented to graphically illustrate the unexpected rise in both the tensile strength and yield point of tempered samples which have been very drastically worked in the metastable austenitic state.

Metallographically, the compositions produced by this invention may be described as an ultra fine grained martensite. The grain size of the martensitic structure which characterizes this invention is reduced by the mechanical deformation to an extent that the grain size in the finished article is less than one-half of the size which would be obtained by the same treatment without the mechanical deformation. A typical individual martensite needle obtained by this invention exhibits a length of about three microns anda thickness of one-half micron. the mechanical deformation these dimensions would be numerically twice as great.

The following compositions were specifically investi- Without In carrying out this invention a suitable steel composition is first austenitized by heating to a suitable temperature and then quickly brought into the selected temperature region by quenching in a liquid maintained at the proper temperature which should fall within the selected temperature region. This temperature region lies between 600 F. and 1100 F. with a preferred range from 800 F. to 1050 F. However, the preferred range may vary according to composition and fabrication techniques. Baths of molten lead or molten salt will serve well for this purpose. When the steel composition has been quenched to the proper temperature it is promptly worked to effect a substantial reduction of area before it has cooled below the selected temperature region into a region in which rapid transformation to bainite or other austenite decomposition products is possible. If the work is very severe, precautions should be taken that the metal is not heated by the energy of the working so as to approach or trespass in the temperature zone in which a transformation into pearlite is possible.

When the desired amount of deformation or work has been accomplished, the steel composition is quenched 'into the martensite transformation zone before any transformation of substance into austenite decomposition products takes place. This quench is into the martensite transformation zone and is sufiiciently drastic to insure a predominantly martensitic microstructure. In most circumstances an ordinary water quench is adequate for this purpose.

The details of this heat treatment and working may more easily be visualized by reference to Figure 1 wherein the experience of the steel mass is traced by the heavy line originating in the upper left hand corner of the drawing and terminating on the abscissa near the ten minute graduation. The deformed horizontal portion of this curve indicates corresponding work.

The martensitic structure obtained by this quenching procedure must be tempered to obtain the optimum final results. Tempering may be accomplished at any temperature desired in the range of 150 F. to 750 F. depending upon the final properties desired. .A progressive increase takes place in the ratio of yield strength to tensile strength as the tempering temperature increases. This ratio is about 0.71 at 150 and increases to 0.93 at 600 F. The preferred tempering range is 350 F. to 700 F.

A reference to the table supra will disclose a substantial silicon content in all of the alloys except the first three. The presence of this element is helpful in permitting tempering and use of the steel in the so-called bluebrittle range of about five hundred degrees to six hundred degrees Fahrenheit and to somewhat mitigate the deleterious effects of tempering upon the tensile strength. The carbon content of the alloys is important. Improvements Martenslte Plate Size (Mlcrons) Deformation 0.31% C 0.41% C 0.47% O In the practice of this invention it is preferred to rely upon chromium or nickel and chromium to stabilize the austenite against premature decomposition. However, it is to be understood that other elements known to have the same effect may also be so employed. Examples of such elements are boron, manganese and nitrogen.

To insure an adequate bay width between the pearlite transformation zone and the bainite transformation zone,

additions of molybdenum may be made. A similar effect may also be had by additions of manganese, vanadium and tungsten.

We claim as our invention:

1. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature sufiicient to render the structure of the steel austenitic, the chemical composition of said steel mass being such that it exhibits a metastable austenite structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region be.ow the temperature at whichaustenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing a substantial amount of work upon the steel mass while maintaining the temperature of the mass within the selected region,'

ucts will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to'narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

2. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature sufficient to render the structure of the steel austenitic, the chemical composition of said steel mass being such that it exhibits a metastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, quenching the austenitic mass sufiiciently drastically to avoid any transformation into pearlite and to bring the mass to the selected.

temperature region without permitting any substantial transformation into bainite, performing SUfliCieHt work upon the steel mass while maintaining the temperature of the steel mass within the selected region to deform the steel mass at least ninetypercent, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of metastable austenite.

3. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature suflicient to render the structure of the steel austenitic, the chemical composition of the steel including sufficient chromium that it exhibits a metastable austenitic structure under conditions of substantial working when quenched froma temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the massto the selected temperature region without permitting any substantial transformation. into bainite, performing a substantial amount of work upon the steel mass whilemaintaining the temperature of the mass within the selected region, said work being sufiicient to effect a deformation of at least twenty-five percent at least locally, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

4. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature suificient to render. the structure of the steel austenitic,

the chemical composition of the steel including sufficientchromium that it exhibits a metastable austenitic structure under conditions of substantial working when into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, quenching the austenitic mass sutficiently to avoid any trans formation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing sufiicient work upon the steel mass while maintaining the temperature of the steel mass within the selected region to deform the steel mass at least ninety percent, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic 7 grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of metastable austenite.

5. The product of forming and heat treating a steel product comprisingheating a steel mass to aitem'perature suflicient' to? render the structureof, the steel austenitic,

the chemical composition of said steel mass being such that it exhibits a mestastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and abovethe temperature at which austenite transforms into bainite within the time necessary for the working process, said selected temperature region extending from six hundred degrees Fahrenheit to one thousand one hundred degrees Fahren heit, quenching theaustenitic mass sufliciently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, per forming a substantial amount of work upon the steel mass while maintaining the temperature of the mass" obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

6. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature suflicient to render the structure of the steel austen itic, the chemical composition of said steel' m'ass' being such that it exhibits a metastable auste'niti'c structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said selected temperature region extending from six hundred degrees Fahrenheit to one thousand one hundred degrees Fahrenheit, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing sufficient work upon the steel mass while maintaining the temperature of the steel mass witli in the selected region to deform the steel mass at least ninety percent, quenching the steel mass from the selected temperature region to a temperature at which the formed directly to martensite without working of metastable austenite.

7. The process of forming and heat treating a steel product comprising heating a steel mass to a tempera-- ture sufficient to render the structure of the steel austenitic, the chemical composition of the steel including sufficient chromium that it exhibits a metastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said selected temperature region extending from sixihundred degrees Fahrenheit to one thousand one hundred.

degrees Fahrenheit, quenching the austenitic mass suf-' ficiently drastically to avoid any transformation, intone assesses pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing a substantial amount of work upon the steel mass while maintaining the temperature of the mass within the selected region, said work being suflicient to effect a deformation of at least twenty-five percent at least locally, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

8. The process of forming andheat treating a steel product comprising heating a steel mass to a temperature sufficient to render the structure of the steel austenitic, the chemical composition of the steel including a sufficient chromium that it exhibits a metastable austenitic structure under conditions of'substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said selected temperature region extending from six hundred degrees Fahrenheit to one thousand one hundred degrees Fahrenheit, quenching the austenitic mass sufi'iciently to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing suflicient work upon the steel mass while maintaining the temperature of the steel mass within the selected region to deform the steel mass at least ninety percent, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size in substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of metastable austenite,

9. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature sufficient to render the structure of the steel austenitic, the chemical composition of said steel mass being such thatit exhibits a metastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said selected temperature region extending from eight hundred degrees Fahrenheit to one thousand fifty degrees Fahrenheit, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing a substantial amount of work upon the steel mass while maintaining the temperature of the mass within the selected region, said work being sufficient to effect a deformation of at least twenty-five percent at least locally, quenching the steel mass from the selected temperature region-to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martenthatvit exhibits a metastable austenite structure underconditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature atwhich austenite transforms into bainite within the time necessary for the Working process, said selected temperature region extending from eight hundred degrees Fahrenheit to one thousand fifty degrees Fahrenheit, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing suflicient work upon the steel mass while maintaining the temperature of the steel mass within the selected region to deform the steel mass at least ninety percent, quenching-the steel mass from the selected temperature region at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of metastable austenite.

11. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature sutficient to render the structure of the steel austenitic, the-chemical composition of the steel including sufficient chromium that it exhibits a metastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said selected temperature region extending from eight hundred degrees Fahrenheit to one thousand fifty degrees Fahrenheit, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing a substantial amount of work upon the steel mass while maintaining the temperature of the mass within the selected region, said work being suflicient to effect a deformation of at least twenty-five percent at least locally, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

12. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature sufficient to render the structure of the steel austenitic, the chemical composition of the steel including sufficient chromium that it exhibits a metastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transformstinto bainite within the time necessary for the working process, said selected temperature region extending from eight hundred degrees Fahrenheit to one thousand fifty degrees Fahrenhit, quenching the austenitic mass sufiiciently to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing suflicient work upon the steel mass while maintaining the temperature of the steel mass within the selected region to deform the steel mass at least ninety percent, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained to increase the yield point and to narrow the range between the yield point and the tensile strength whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of meta: stable austenite.

13. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature sufi'icient to render the structure of the steel austenitic, the chemical composition of the said steel mass being such that it exhibits a metastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and abovethe temperature at which austenite transforms into bainite within the time necessary for the working process, said temperature region extending from six hundred degrees Fahrenheit to one thousand one hundred degrees Fahrenheit, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing a substantial amount of work upon the steel mass while maintaining the temperature of the mass within the selected temperature region, said work being sufficient to effect a deformation of at least twenty-five percent at least locally, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained at a temperature falling within the range of one hundred fifty degrees Fahrenheit to seven hundred fifty degrees Fahrenheit to increase the yield point and to narrow the range between the yield point and the tensile strength, whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformeddirectly to martensite without working of the metastable austenite.

14. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature suflicient to render the structure of the steel austenitic, the chemical composition of the said steel mass being such that it exhibits a metastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature, region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said temperature region extending from eighthundred degrees Fahrenheit to one thousand fifty degrees Fahrenheit, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing a substantial amount of work upon the steel mass while maintaining the temperature of the mass with- 10 inrthe selected temperature region, said work being suf= ficient to deform the steel mass at least ninety percent, quenching the steel mass from the selectedtemperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and,

tempering the martensitic structure so obtained at a temperature falling within the range of three hundred fifty to seven hundred degrees Fahrenheit to increase the yield point and to narrow the range between the yield point and the tensile strength, whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

15. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature sufiicient to render the structure of the steel austenitic, the chemical composition of the said steel mass including suflicient chromium so that it exhibits a metastable austenic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said temperature region extending from six hundred degrees Fahrenheit to one thousand one hundred degrees Fahrenheit, quenching the austenitic mass sufficiently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing a substantial amount of work upon the steel mass while maintaining the temperature; of the mass within the selected temperature region, said work being sufiicient to efiect a deformation of at least twenty-five percent at least locally, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained at a temperature falling within the range of one hundred fifty to seven hundred fifty degrees Fahrenheit to increase the yield point and to narrow the range between the yield point and the tensile strength, whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

16. The process of forming and heat treating a steel product comprising heating a steel mass to a temperature sufficient to render the structure of the steel austenitic, the chemical composition of the said steel mass including sufiicient chromium so that it exhibits a metastable austenitic structure under conditions of substantial working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said temperature region extending from six hundred degrees Fahrenheit to one thousand one hundred degrees Fahrenheit, quenching the austenitic mass sufiiciently drastically to avoid any transformation into pearlite and to bring the mass to the selected temperature region without permitting any substantial transformation into bainite, performing a substantial amount of work upon the steel mass while maintaining the temperature of the mass within the selected temperature region, said work being suflicient to deform the steel mass at least ninety percent, quenching the steel mass from the selected temperature region to a temperature at which the isothermal transformation products will be predominantly martensitic and tempering the martensitic structure so obtained at a temperature falling within the range of one hundred fifty to seven hundred fifty degrees Fahrenheit to increase the yield point and to narrow the range between the yield point and the tensile strength, whereby a fine grained martensitic product is obtained in which the martensitic grain size is substantially smaller than the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

17. The process of producing a steel product having a minimum dimension of at least one-eighth inch, the microstructure of which is tempered martensite, comprising selecting a steel composition exhibiting a metastable austenitic structure under conditions of working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, heating the steel composition to render it stably austenitic, quenching the austenitized hardenable alloy steel composition sufficiently drastically to avoid any transformation into pearlite and to bring the composition to the selected temperature region, performing a substantial amount of work upon the steel composition while maintaining it in said selected temperature region until the substantial amount of work has been completed, said work being sufiicient to effect a deformation of at least twenty-five percent, quenching the composition from the selected temperature region to a temperature at which the transformation products Will consist essentially of martensite, said quenching operation being sufiiciently drastic to insure a structure consisting essentially of martensite, and tempering the martensitic structure so obtained to narrow the range between the yield point and the tensile strength and to enhance the ductility, whereby a product is obtained in which the martensitic grain size is not over one-half of the martensitic grain size of the same steel if transformed directly to martensite without working of the metastable austenite.

18. The process of producing a steel product having a minimum dimension of at least one-eighth inch, the microstructure of whichis tempered martensite, comprising selecting a steel composition comprising carbon 0.10 percent to 0.80 percent, nickel 2 percent to 6percent, and chromium 0.75 percent to 3.0 percent and exhibiting a metastable austenitic structure under conditions of working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, heating the steel composition to render it stably austenitic, quenching the austenitized hardenable alloy steel composition sufficiently drastically to avoid any transformation into pearlite and to bring the composition to the selected temperature region, performing a substantial amount of work upon the steel composition while maintaining it in said selected temperature region until the substantial amount of work has been completed, said work being sufficient to effect a deformation of at least twenty-five percent, quenching the composition from the selected temperature region to a temperature at which the transformation products will consist essentially of mar tensite, said quenching operation being sufficiently drastic to insure a structure consisting essentially of martensite, and tempering the martensitic structure so obtained.

19. The process of producing a steel product having a minimum dimension of at least one-eighth inch, the microstructure of which is tempered martensite, comprising selecting a steel composition exhibiting a metastable austenitic structure under conditions of working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, said selected temperature region comprising the range extending from six hundred degrees Fahrenheit to one thousand one hundred degrees Fahrenheit, heating the steel composition to render it stably austenitic, quenching the austenitized composition sufficiently drastically to avoid any transformation into pearlite and to bring the composition to the selected temperature region, performing a substantial amount of work upon the steel composition while maintaining it in said selected temperature region until the substantial amount of work has been completed, said work being suflicient to effect a deformation of at least twenty-five percent at least locally, quenching the composition from the selected temperature region to a temperature at which the transformation products will consist essentially of martensite, said quenching operation being sufficiently drastic to insure a structure con sisting essentially of martensite, and tempering the martensitic structure so obtained at a temperature in the range of one hundred fifty degrees Fahrenheit to seven hundred fifty degrees Fahrenheit.

20. The product produced by the process of claim 19, which product is metallographically indistinguishable from that depicted in Figure land which consists essentially of a very fine grained tempered martensite.

21. The product produced by the process of claim 1, which product consists essentially of a very fine grained tempered martensite. v

22. The process of producing a steel product having a minimum dimension of at least one-eighth inch, the microstructure of which is tempered martensite, comprising selecting a steel composition exhibiting a metastable austenitic structure under conditions of working when quenched from a temperature at which austenite is stable into a selected temperature region below the temperature at which austenite transforms into pearlite and above the temperature at which austenite transforms into bainite within the time necessary for the working process, heating the'steel composition to render it stably austenitic, quenching the austenitized hardenable alloy steel composition sufficiently drastically to avoid any transformation into pearlite and to bring the composition to the selected temperature region, performing a substantial amount of work upon the steel composition while maintaining it in saidselected temperature region until the substantial amount of Work has been completed, said work being sufiicientto effect a deformation of at least ninety percent, quenching the composition from the selected temperature region to a temperature at which the transformation products will consist'essentially of martensite, said quenching operation being sufficiently drastic to insure a structure consisting essentially of martensite, and tempering the martensitic structure so obtained.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN Patent No. 2,934,463

Duane J, Schmatz et a1.

April 26, 1960 s in the printed specification It is hereby certified that error appear tion and that the said Letters I of the above numbered patent requiring correc Patent should read as corrected below.

Column 2, line 57, after "tempering" insert temperature column 7, line 44, for "in" read 1s Signed and sealed this 20th day of December 1960.

(SEAL) Attest:

KARL H. AXLINE Attesting Officer ROBERT C. WATSGN Commissioner of Patents 

19. THE PROCESS OF PRODUCING A STEEL PRODUCT HAVING A MINIMUM DIMENSION OF AT LEAST ONE EIGHTH INCH, THE MICROSTRUCTURE OF WHICH IS TEMPERED MARTENSITE, COMPRISING SELECTING A STEEL COMPOSITION EXHIBITING A METASTABLE AUSTENITIC STRUCTURE UNDER CONDITIONS OF WORKING WHEN QUENCHED FROM A TEMPERATURE AT WHICH AUSTENITE IS STABLE INTO A SELECTED TEMPERATURE REGION BELOW THE TEMPERATURE AT WHICH AUSTENITE TRANSFORM IN TO PEARLITE AND ABOVE THE TEMPERATURE AT WHICH AUSTENITE TRANSFORM INTO BAINITE WITHIN THE TIME NECESSARY FOR THE WORKING PROCESS, SAID SELECTED TEMPERATURE REGION COMPRISING THE RANGE EXTENDING FROM SIX HUNDRED DEGREES FAHRENHEIT, HEATING ONE THOUSAND ONE HUNDRED DEGREES FAHRENHEIT, HEATING THE STEEL COMPOSITION TO RENDER IT STABLY AUSTENITIC, QUENCHING THE AUSTENITIZED COMPOSITION SUFFICIENTLY DRASTICALLY TO AVOID ANY TRNASFORMATION INTO PERALITE AND TO BRING THE COMPOSITION TO THE SELECTED TEMPERATURE REGION, PERFORM- 